Not Applicable.
Not Applicable.
The present invention relates generally to vehicle wheel alignment sensors of the type which are pendulously secured to a vehicle wheel by a mounting shaft during a vehicle wheel alignment procedure, and in particular, to an apparatus and method for identifying and tracking the absolute mounting shaft rotational position of the vehicle wheel alignment sensor after it has been mounted to a vehicle wheel.
Computer controlled vehicle wheel alignment systems, such as those shown in U.S. Reissue Pat. No. 33,144 to Hunter et al., U.S. Pat. No. 4,381,548 to Grossman et al., and U.S. Pat. No. 5,598,357 to Colarelli et al., utilize a number of wheel-mounted alignment sensors, such as those described in U.S. Pat. No. 4,879,670 to Colarelli, to obtain measurements related to vehicle wheel alignment parameters. The majority of vehicle wheel alignment sensors currently utilized in the market are xe2x80x9ccordlessxe2x80x9d, relying on internal rechargeable batteries to power associated circuitry, and communicating to a console wheel alignment computer using conventional wireless communications technology. One example of a conventional computer controlled vehicle wheel alignment system is the Series 811 console, which utilizes the DSP-500 series cordless vehicle wheel alignment sensors, and is sold by Hunter Engineering Company of Bridgeton, Miss.
It is known in the industry that vehicle wheel alignment sensors which are pendulously secured to individual vehicle wheels must be compensated for any runout present between a plane in which the vehicle wheel alignment sensor hangs, and a plane perpendicular to the rotational axis of the wheel. The preferred procedures for obtaining runout compensation generally involve mounting a vehicle wheel alignment sensor to a vehicle wheel using a wheel clamp, rotating the wheel and mounting shaft to three distinct rotational positions relative to the sensor housing, and obtaining sensor readings for each position. Using the three sensor readings, a sinusoidal pattern representative of the amount of runout present between the vehicle wheel alignment sensor and the vehicle wheel may be calculated for any rotational position of the vehicle wheel and/or sensor. This runout compensation procedure for a vehicle wheel alignment sensor is described in detail in U.S. Pat. No. 5,052,111 to Carter et al.
Once the runout compensation procedure has been successfully completed, the vehicle wheel alignment sensor establishes a relative base rotational position of the mounting shaft. Utilizing an inexpensive relative rotational position sensor, the vehicle wheel alignment sensor tracks the rotation of the mounting shaft relative to the base rotational position. By tracking the change in the rotational position of the vehicle wheel alignment sensor from the base position, a runout compensation value for the current rotational position of the is calculated from the previously obtained sinusoidal pattern.
One drawback to using inexpensive relative rotational position sensors is an inability of the sensor to identify an absolute rotational position of the vehicle wheel alignment sensor if the established base rotational position is lost. The established base rotational position in a conventional vehicle wheel alignment sensor can become lost for a number of reasons. For example, if the rechargeable batteries supplying power to maintain the wheel alignment sensor memory fail, or require replacement or recharging, data stored in the memory such as the established base rotational position and sinusoidal pattern will be lost, requiring an operator to repeat the time consuming compensation procedure before vehicle wheel alignment can be resumed. Similarly, in rare cases, battery supplied power can be lost momentarily due to poor or unclean battery contacts.
Even if the data values are stored in a persistent memory, such as one receiving power from a capacitor, which will maintain the data values for a limited period of time until the restoration of the normal power supply, any relative rotational movement between the vehicle wheel alignment sensor, mounting shaft, or vehicle wheel will not be recorded by the relative rotational position sensor, resulting in a discrepancy between the rotational position in which the sensor was compensated, and the current rotational position as identified by the relative rotational position sensor upon restoration of power. Finally, if an operator desires to suspend work on a vehicle in the middle of a vehicle wheel alignment procedure, and shuts down the alignment system (such as overnight), the stored data may be lost, and any rotational movement of the mounting shaft relative to the vehicle wheel alignment sensor will not be tracked, requiring the runout compensation procedures to be repeated upon the subsequent system startup.
It is known that an absolute rotational position sensor may be utilized in place of the relative rotational position sensor in a cordless vehicle wheel alignment sensor. An absolute rotational position sensor relies upon unique identification markings associated with the mounting shaft to identify the current absolute rotational position of a fixed point on the mounting shaft relative to the vehicle wheel alignment sensor. However, to align modern vehicles, a very high degree of precision is required in the sensor rotational position measurements. When utilizing an absolute rotational position sensor in such a high precision environment, the sensor must be capable of identifying rotational positions to the same degree of accuracy, and therefore requires a number of unique markings proportional to the required degree of accuracy. Absolute rotational position sensors capable of measuring rotational positions to the required accuracy levels for vehicle wheel alignment are delicate and costly items, and are generally unsuited for use in a vehicle service environment.
Accordingly, there is a need in the industry for an alternative device and method for maintaining cordless vehicle wheel alignment sensor runout compensation values and rotational positions following momentary or extended losses of power, which do not rely upon the use of delicate and costly absolute rotational position sensors in the vehicle wheel alignment sensor.
Briefly stated, an apparatus of the present invention incorporated into a conventional cordless vehicle wheel alignment sensor consists of a photo-interruptive sensor and an associated interrupter disk configured to operate in conjunction with a conventional relative rotational position sensor to provide an absolute rotational position of the mounting shaft relative to the vehicle wheel alignment sensor. The interrupter disk is secured to the mounting shaft of the vehicle wheel alignment sensor, and the photo-interruptive sensor is secured to the body of the vehicle wheel alignment sensor, in operative relationship to the interrupter disk. The interrupter disk is configured with a raised peripheral lip having multiple gaps and teeth, each having a unique size. Signals from the photo-interruptive sensor, together with relative rotational position signals from the relative rotational position sensor in operative relationship to the mounting shaft, are conveyed to a sensor processor and utilized to store, in a sensor memory area, one or more absolute mounting shaft rotational positions. An internal power source, such as a capacitor maintains the integrity of the sensor memory for a definite span of time during momentary power losses such as battery changes or during overnight shutdowns, permitting the mounting shaft runout compensation values to be maintained and reutilized upon the restoration of system power, without the need to repeat the runout compensation procedures.
As a method, the present invention requires a vehicle wheel alignment sensor which has been previously mounted to a vehicle wheel and compensated for runout. To restore or identify an absolute rotational position of the mounting shaft relative to the vehicle wheel alignment sensor, the sensor is rotated about the mounting shaft through at least an arc sufficient to completely traverse at least one uniquely sized tooth or gap on an interrupter disk associated with the mounting shaft. Signals from a photo-interruptive sensor, together with a relative rotational position sensor signal, identify the unique size of the traversed tooth or gap on the interrupter disk. The identified unique size of the traversed tooth or gap is compared with permanently stored information to identify the current absolute rotational position of the vehicle wheel alignment sensor mounting shaft. The current absolute rotational position is then utilized to determine the associated runout compensation value for the current sensor rotational position, using data stored in a persistent sensor memory during a runout compensation procedure, thereby permitting an operator to return the vehicle wheel alignment sensor to a previous rotational position or utilize stored runout compensation data following a general power-down or momentary power loss, such as battery contact failure or during battery replacement or recharging.
The foregoing and other objects, features, and advantages of the invention as well as presently preferred embodiments thereof will become more apparent from the reading of the following description in connection with the accompanying drawings.